gnu.crypto.mode
Class CTR

java.lang.Object
  gnu.crypto.mode.BaseMode
      gnu.crypto.mode.CTR

All Implemented Interfaces:

java.lang.Cloneable, IBlockCipher, IMode

public class CTR

extends BaseMode

implements java.lang.Cloneable

The implementation of the Counter Mode.

The algorithm steps are formally described as follows:

    CTR Encryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    C[j] = P[j] ^ O[j]; for j = 1, 2...n.
    CTR Decryption: O[j] = E(K)(T[j]); for j = 1, 2...n;
                    P[j] = C[j] ^ O[j]; for j = 1, 2...n.
 

where P is the plaintext, C is the ciphertext, E(K) is the underlying block cipher encryption function parametrised with the session key K, and T is the Counter.

This implementation, uses a standard incrementing function with a step of 1, and an initial value similar to that described in the NIST document.

References:

1. Recommendation for Block Cipher Modes of Operation Methods and Techniques, Morris Dworkin.

Version:

$Revision: 1.2 $

Field Summary

Fields inherited from class gnu.crypto.mode.BaseMode

cipher, cipherBlockSize, iv, lock, modeBlockSize, name, state

Fields inherited from interface gnu.crypto.mode.IMode

DECRYPTION, ENCRYPTION, IV, MODE_BLOCK_SIZE, STATE

Fields inherited from interface gnu.crypto.cipher.IBlockCipher

CIPHER_BLOCK_SIZE, KEY_MATERIAL

Constructor Summary

(package private)

CTR(IBlockCipher underlyingCipher, int cipherBlockSize) Trivial package-private constructor for use by the Factory class.

Method Summary

java.lang.Object	clone() Returns a clone of this instance.
void	decryptBlock(byte[] in, int i, byte[] out, int o) Decrypts exactly one block of ciphertext.
void	encryptBlock(byte[] in, int i, byte[] out, int o) Encrypts exactly one block of plaintext.
void	setup() The initialisation phase of the concrete mode implementation.
void	teardown() The termination phase of the concrete mode implementation.

Methods inherited from class gnu.crypto.mode.BaseMode

blockSizes, currentBlockSize, defaultBlockSize, defaultKeySize, init, keySizes, name, reset, selfTest, update

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CTR

CTR(IBlockCipher underlyingCipher,
    int cipherBlockSize)

Trivial package-private constructor for use by the Factory class.

Parameters:

underlyingCipher - the underlying cipher implementation.

cipherBlockSize - the underlying cipher block size to use.

Method Detail

clone

public java.lang.Object clone()

Description copied from interface: IBlockCipher

Returns a clone of this instance.

Specified by:

clone in interface IBlockCipher

Specified by:

clone in class BaseMode

setup

public void setup()

Description copied from class: BaseMode

The initialisation phase of the concrete mode implementation.

Specified by:

setup in class BaseMode

teardown

public void teardown()

Description copied from class: BaseMode

The termination phase of the concrete mode implementation.

Specified by:

teardown in class BaseMode

encryptBlock

public void encryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)

Description copied from interface: IBlockCipher

Encrypts exactly one block of plaintext.

Specified by:

encryptBlock in interface IBlockCipher

Specified by:

encryptBlock in class BaseMode

decryptBlock

public void decryptBlock(byte[] in,
                         int i,
                         byte[] out,
                         int o)

Description copied from interface: IBlockCipher

Decrypts exactly one block of ciphertext.

Specified by:

decryptBlock in interface IBlockCipher

Specified by:

decryptBlock in class BaseMode